This invention relates to a monitoring system that automatically displays still images related to an intrusion alarm in order to enhance the ability of security personnel to assess the nature of the alarm.
Intrusion detection systems are widely used to control and monitor access to sensitive areas such as for example commercial nuclear generating stations. Typically, such detection systems will monitor a perimeter divided into zones. Each zone will have one or more sensors designed to detect intrusion into the zone as well as one or more video cameras positioned to observe an intruder who has triggered a sensor in the respective zone.
FIG. 1 shows a schematic representation of one such prior art intrusion detection system. The system of FIG. 1 monitors a portion of a perimeter which includes three zones: Zone 1, Zone 2, Zone 3. Each of the zones is at least partially defined by a respective one of two perimeter fences 10, 12. As shown in FIG. 1, three sensor systems S1, S2, S3 monitor the respective zones, and each of the sensor systems S1, S2 S3 generates a respective alarm signal A1, A2, A3 when triggered. The sensor systems S1, S2, S3 may include either active sensors, passive sensors, or some combination. Active sensors such as microwave sensors detect intrusions by sensing changes in an energy field generated by the sensor. Passive sensors, such as heat detectors, sense intrusions by detecting environmental changes such as the heat associated with a person or other intruder. Further details on such sensors may be found in R. L. Barnard, Intrusion Detection Systems (2nd Edition, 1988) at pages 19-21.
The system of FIG. 1 further includes a number of video cameras VC1-VC6 that generate respective video signals V1-V6. In the illustrated system there are two video cameras associated with each of the zones, and the video cameras may be positioned either inside or outside the respective zone. Any number of cameras may be used to cover a zone, depending upon the physical characteristics of the zone and good security practice, and the number of video cameras used per zone may be either greater or lesser than the number shown in FIG. 1. The cameras may be any conventional video camera that generates a standard RS170 signal. However, higher quality cameras will generate better pictures because they operate with a greater bandwidth that allows more levels of gray to be used in the final digitized picture described below.
In the past, intrusion detection systems have been used in which a central control system automatically responds to the alarm signals A1-A3 to record on video tape the video signals V1-V6 associated with the zone in which the intrusion was detected. The security guard is then expected to rewind the video cassette recorder to view the zone at the time of the intrusion. This approach relies on the security guard to rewind the VCR and to view the recorded video images for each alarm. In the event there are a number of false alarms, the security guard may not always choose to complete the time consuming job of rewinding the VCR and then watching it. Furthermore, a VCR that stores a conventional video image is not well suited to record quickly changing scenes. In the event of a moving car passing through a zone, only a few frames may have sufficient detail to allow details such as the license number of the car to be seen.
Another problem encountered with previous video monitoring systems is that in the event of multiple alarms the first alarm may impede or prevent the security guard from viewing video information regarding subsequent alarms. This weakness can be exploited by false alarms which may delay or prevent the security guard from seeing the real intrusion.
Yet another problem of certain prior art intrusion detection systems is related to the fact that alarm signals may not be reported at the central station promptly. In this case, a quickly changing scene may have changed substantially before the controller can begin to record video signals from the appropriate video cameras. When this happens critical information that would be useful to a security guard in assessing an alarm is irretrievably lost.
Accordingly, it is a primary object of this invention to provide an improved intrusion detection system which automatically displays still video images of a zone associated with an alarm to allow a security guard to assess the alarm.
It is a further object of this invention to provide such a system in which multiple still video images corresponding to multiple successive alarms are stored and readily accessible to a security guard. This allows the security guard to view still video images associated with successive alarms quickly and easily.
It is another object of this invention to provide such an intrusion detection system which stores still video images associated with an alarm prior to reception of the alarm by a central control system for automatic retrieval and display in the event of an alarm.
It is another object to provide such a system in which the magnification and contrast of the displayed video images can be adjusted easily by a security guard.